Synchronous vs. Asynchronous link. What are they? How they are different? Is synchronous always better than asynchronous link? Do I need to choose which one I want to use? Or it depends on link type? Ex. Dial-up and ISDN are synchronous?
The difference between the two, it's that one transmit and receive at the same speed (Synchronous) while the other transmit and receive at different speeds (Asynchronous).
Synchronous is better but it comes with a price. Asynchronous allows you to purchase more bandwidth for the money at the expense of lower upload speeds.
Dial-Up and ISDN are Synchronous.
ADSL is Asynchronous.
I am sorry but ADSL is not Asyncronous. It is syncronous and stands for Asymetrical DSL. It means that the download speed is larger then the upload speed. Sycronous means that the clocking of the data is transmitted with the data. Asyncronous the clocking mechanisms are independant at both ends. Asyncronous data has a start stop and parity bit in its data word. Syncronous works well with the high speed data protocols such as HDLC, PPP,SDLC,SONET etc.. Async is predominantly used for lower speeds....
I know you posted this 8 years ago but thanks... it really helped make sense of the Syncronous/Asynchronous question... learning that protocols and encapsulation all involve what the packets and frames tell about the speed it wants to travel across Layer1 from one end to the other... how much data it's carrying, ack bits and how the next sequence is calculated into the headers... all of it... it's so much to learn and having an answer like that fits into what we're learning about the bigger picture so thanks.
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BTW, you might also want to know, synchronous generally uses less bandwidth to transmit data than asynchronous. You might also want to know when we talk of link "speed", it's really bandwidth, or capacity. I.e. how much data we can move in some unit of time; not quite the same as how quickly it will arrive. This distinction is important when dealing with long distance links, i.e. increasing bandwidth ("speed") often offers little improvement for applications being impacted by distance based latency.